The invention relates to a new type of use for a ceramic composition to protect glassware from corrosion during washing and/or rinsing cycles of a dishwasher, compositions intended for use in a dishwasher for the aforesaid purpose, and a method of inhibiting the corrosion of glassware during washing and/or rinsing cycles of a dishwasher.
The problem of glassware corroding during washing and/or rinsing cycles of a dishwasher has long been known. Current opinion is that the problem of corrosion in glassware is the result of two separate phenomena. On the one hand, the corrosion is clearly due to minerals from the glass composition accompanied by hydrolysis of the silicate network. On the other hand, silicate material is released from the glass. After several washes in a dishwasher, both phenomena can cause damage to glassware, such as cloudiness, scratches, streaks, and the like.
Silicate compounds are known to be effective in preventing minerals from being released from the glass composition, but on the other hand can tend to increase the separation of silicate material at the surface of the glass.
Various proposals have been put forward as a means of dealing with the problems described above.
One approach is to use zinc, either in metallic form (U.S. Pat. No. 3,677,820) or in the form of zinc compounds. The use of soluble zinc salts as a means of preventing the corrosion of glassware in dishwasher cleansers is described in U.S. Pat. No. 3,255,117, for example.
Because of a number of disadvantages inherent in using soluble zinc salts (in particular the formation of a precipitate of insoluble zinc salts with other ions in the washing or rinsing water), European patent applications EP 0 383 480, EP 0 383 482 and EP 0 387 997 propose the use of insoluble zinc compounds as a means of inhibiting corrosion of glassware in automatic dishwashers. Specifically, the insoluble zinc salts proposed are zinc silicate, zinc carbonate, zinc oxide, basic zinc carbonate (approximately: Zn2(OH)2CO3), zinc hydroxide, zinc oxalate, zinc monophosphate (Zn3(PO4)2), and zinc pyrophosphate (Zn2(P2O7)). If using zinc salts of this type in granular cleansing compounds, the insoluble zinc compound is specified as having a maximum particle size of less than 1.7 mm (EP 0 383 482), while a mean particle size of less than 250 xcexcm is specified for the insoluble zinc compound used in a liquid dishwasher composition (EP 0 383 480 and EP 0 387 997).
The disadvantage of the prior art essentially resides in the fact that, because the zinc compounds are not readily soluble or are insoluble, it is difficult to ensure that a sufficient quantity of active agent will be present in the washing or rinsing liquid to protect glassware from corrosion. Furthermore, in view of the high specific density of the insoluble zinc compounds listed, problems of separation arise with powdered mixtures or settlement in the case of liquid mixtures. Finally, all of the known compositions are intended to be active during only one specific stage of the washing cycle, i.e., if admixed with a granular cleanser composition during the washing cycle or if admixed with a liquid rinsing composition with the rinsing cycle. None of the known compositions has the capacity to become and remain active starting from the washing cycle and/or one of the intermediate rinsing cycles onwards
The underlying objective of the present invention is to resolve at least one and preferably all of the existing problems outlined above.
This objective is achieved by the invention by the use of a ceramic composition to protect glassware from corrosion, the ceramic composition being made using at least one compound which releases an active anti-corrosion agent during the washing and/or rinsing cycles of a dishwasher.
By preference, the compound(s) which release(s) an active agent to prevent corrosion during washing and/or rinsing cycles of a dishwasher is/are selected from the group consisting of the oxides of zinc, aluminum, tin, magnesium, calcium, strontium, silicon, titanium, zirconium, manganese, and/or lanthanum, and/or precursors thereof. In one specific embodiment, the invention proposes that at least one of the compounds used should be zinc oxide and/or a precursor thereof.
By preference, the ceramic composition is used in tablet form. Alternatively, the ceramic composition is used in crushed form, and more preferably in ground form. The ground ceramic composition preferably has an average particle size of at most about 500 xcexcm.
The invention also relates to a composition for use in a dishwasher which contains an active quantity of a ceramic composition in crushed form to protect glassware against corrosion, the ceramic composition being made using at least one compound which releases an active agent to protect glassware from corrosion during washing and/or rinsing cycles of a dishwasher.
The ceramic composition is preferably used in ground form, more preferably with a mean particle size of at most about 500 xcexcm.
The composition proposed by the invention preferably contains the crushed ceramic composition in a quantity of about 0.1 to 10% by weight, more preferably in a quantity of about 0.5 to 5% by weight.
The invention also relates to a composition for use in a dishwasher in the form of a tablet containing an active quantity of a ceramic composition to protect glassware against corrosion, the ceramic composition being made using at least one compound which releases an active agent during washing and/or rinsing cycles of a dishwasher to protect glassware from corrosion.
In one embodiment, the invention proposes that the compound(s) which release(s) an active agent to protect glassware from corrosion during washing and/or rinsing cycles of a dishwasher should be selected from the group consisting of the oxides of zinc, aluminum, tin, magnesium, calcium, strontium, silicon, titanium, zirconium, manganese, and/or lanthanum. In one particular embodiment, the invention proposes that at least one of the compounds should be zinc oxide and/or a precursor thereof.
Finally, the invention relates to a method of inhibiting the corrosion of glassware during washing and/or rinsing cycles of a dishwasher, characterized by the glassware being brought into contact with washing or rinsing water containing an active quantity of the aforesaid composition containing a crushed ceramic composition.
Alternatively, a method of inhibiting the corrosion of glassware during washing and/or rinsing cycles of a dishwasher is proposed, in which the composition described above containing the ceramic composition is provided in tablet form, placed in the interior of the dishwasher at a point which is accessible to the washing and/or rinsing water.
Before giving a detailed explanation of the features and advantages of the present invention, it should be pointed out that for the purpose of the present invention, the concept xe2x80x9cceramic compositionxe2x80x9d should be construed in its broadest sense, namely all materials made up of inorganic and predominantly non-metallic compounds or elements that are crystalline by reference to more than 30% by volume, in particular but not restricted to clay ceramic substances but also glass ceramic substances, for example.
The present invention solves at least one, and in preferred embodiments all the problems inherent in the prior art described above.
By using a ceramic substance as a xe2x80x9cbasexe2x80x9d for one or more reagents to protect glassware from corrosion in a dishwasher, the problem caused by the extensive formation of precipitate from insoluble salts which result in an undesirable deposit, such as occurs with the prior art due to the use of soluble zinc salts for this purpose, are avoided. Instead, the active agents, such as zinc ions, are released from the ceramic compound proposed by the invention into the washing or rinsing water in a delayed release pattern but are not present in a high enough concentration to lead to an extensive and undesirable formation of insoluble salts. The disadvantages of using insoluble zinc compounds described above are avoided by using the ceramic compositions proposed by the invention.
By using the ceramic composition proposed by the invention in ground form as an additive to standard dishwasher products, which are generally made as powders or liquids, the problem of separation described above is also resolved, since the use of a ceramic composition offers greater flexibility in terms of adjusting the specific density requirements.
If the ceramic composition proposed by the invention is provided in tablet form and placed in the interior of the dishwasher at a point which is accessible to the washing and/or rinsing water, e.g. in the cutlery basket, it will also provide, for the first time ever, active protection against corrosion throughout all washing and rinsing cycles, i.e., from the pre-rinse cycle through to the cleaning cycle and then the intermediate rinse cycles through to the final rinse cycle and, what is more, will last for several cycles. As a result, not only is glassware thoroughly protected against corrosion in the dishwasher, handling is made significantly easier and more convenient for the consumer.
If the ceramic composition proposed by the invention is used in crushed form, it may be ground in a grinder specifically suited to this purpose, for example, and an appropriate fraction of particles separated out, e.g. having an average grain particle of at most about 500 xcexcm.
The features of the invention disclosed in the description above and in the claims may be used individually or in any combination to apply the invention in its different embodiments.